The present invention relates to semiconductor design technology, and more particularly, to a piecewise linear processing device for applying different amplification rates according to a general environment and a low luminance environment where much noise exists.
To reinforce a conventional piecewise linear processing method used for a gamma correction circuit and a contrast correction circuit in an image processing, the present invention provides a function that can be provided to an image signal processor (ISP) mounted in a complementary metal oxide semiconductor (CMOS) image sensor.
The function will be described in detail with reference to FIGS. 1A and 1B.
FIG. 1A is a graph illustrating a function used for a conventional piecewise linear processing device, illustrating a level of an output data with respect to an input data.
Referring to FIG. 1A, the piecewise linear processing device amplifies an input signal in a low code region with a high amplification rate and amplifies an input signal in a high code region with a relatively low amplification rate so as to make up for identifying ability.
When processing actual input signals, the piecewise linear processing device uses the linear function divided into a plurality of sections as illustrated in FIG. 1B. A knee point defining each section is set by a user. The conventional piecewise linear processing device using the linear function applies an amplification rate of a relevant section to the corresponding input data IN_FX_DT to output as the output data OUT_FX_DT.
The piecewise linear processing device uses the plurality of linear functions illustrated in FIG. 1B because of a limitation in a semiconductor area. In other words, when a hardware is realized to process an input signal through a function curve illustrated in FIG. 1A, a large area is required, which means the increase of a manufacturing cost. Therefore, a hardware processes an input signal using the linear function (shown in FIG. 1B) realized by dividing the curve function into a plurality of sections, instead of the curve function of FIG. 1A.
For reference, the above-described piecewise linear processing device is used for a gamma correction circuit and a contrast correction circuit inside an image processing device. The piecewise linear processing device can be used for a charged coupled device (CCD) image processing device, and used for all image circuits and processing devices where a piecewise linear processing method is used. Description will be made with reference to FIG. 2.
FIG. 2 is a block diagram of a conventional piecewise linear processing device, which has an operation curve such as the linear function illustrated in FIG. 1B.
Referring to FIG. 2, the conventional piecewise linear processing device includes a default knee point storing unit 10 for storing a user's default setting value Am, and a piecewise linear processing unit 20 for applying a section amplification rate to input data IN_FX_DT on the basis of regions defined by knee points of the default knee point storing unit 10 to output the output data OUT_FX_DT.
An operation will be briefly described below. When the user applies a default setting value Am on the basis of a general environment, the default knee point storing unit 10 stores the value.
The piecewise linear processing unit 20 receives the knee points of the default knee point storing unit 10, and applies a section amplification rate corresponding to the knee point to the input data IN_FX_DT to output the output data OUT_FX_DT.
As described above, the conventional linear processing device collectively applies the default setting value Am applied on the basis of a general environment to all the environments to process the input data IN_FX_DT.
Meanwhile, since a noise in a low code band of the input data IN_FX_DT is amplified at a large amplification rate under a low luminance environment where much noise exists, an entire screen noise increases.
A conventional piecewise linear processing device using different linear functions for a general environment and a low luminance environment will be described with reference to FIG. 3.
FIG. 3 is a block diagram of another conventional piecewise linear processing device.
Referring to FIG. 3, the conventional piecewise linear processing device includes a default knee point storing unit 30 for storing a user's default setting value Am and a low luminance setting value Bm, a luminance detecting unit 40 for detecting a low luminance environment to output a control signal, an output control unit 50 for outputting the default setting value Am or the low luminance setting value Bm as a knee point in response to the control signal, and a piecewise linear processing unit 60 for applying a section amplification rate to the input data IN_FX_DT on a region corresponding to the knee point to output the output data OUT_FX_DT.
The default knee point storing unit 30 includes a first knee point storing unit 32 for storing an applied default setting value Am, and a second knee point storing unit 34 for storing a low luminance setting value Bm.
As described above, the conventional piecewise linear processing device receives the low luminance setting value Bm used for a low luminance environment, and uses the low luminance setting value Bm as a knee point under the low luminance environment in response to the control of the luminance detecting unit 40. Therefore, the piecewise linear processing device of FIG. 3 solves a limitation that noise is amplified in a low luminance region compared to the piecewise linear processing device of FIG. 2.
FIG. 4 is a graph illustrating the linear function of the piecewise linear processing device of FIG. 3.
When a user applies a default setting value Am and a low luminance setting value Bm, they are stored in corresponding knee storing units 32 and 34, respectively. Under a general environment, the piecewise linear processing unit 60 receives as a knee point the default setting value Am that is provided by the output control unit 50 and stored in the first knee point storing unit 32. Also, the piecewise linear processing unit 60 applies a relevant section amplification rate to the input data IN_FX_DT on the basis of a knee point corresponding to the default setting value Am to output the output data OUT_FX_DT. That is, under a general environment, the piecewise linear processing device has a linear function including A0-A6 such as the default setting value Am.
Meanwhile, under the low luminance environment, the luminance detecting unit 40 detects the low luminance environment to activate a control signal. The output control unit 50 outputs the low luminance setting value Bm stored in the second knee point storing unit 34 as a knee point in response to the control signal. The piecewise linear processing unit 60 applies a relevant section amplification rate to the input data IN_FX_DT on the basis of a knee point corresponding to the low luminance setting value Bm to output the output data OUT_FX_DT. Therefore, under the low luminance environment, the piecewise linear processing device has a linear function including B0-B6 such as the low luminance setting value Bm.
Meanwhile, a change in the linear function is described in an aspect of an output range versus an input range such as a region A. First, a difference between two input values on an X-axis of the linear function is the input range, and a difference between two output values on a Y-axis of the linear function is the output range. The region A represents an output range versus an input range corresponding to the points A0 and A1 of the linear function for the general environment. Comparison of an output range versus an input range under the general environment with an output range versus an input range under the low luminance environment shows that a ratio of an output range to an input range reduces under the low luminance environment. As described above, an influence by noise is reduced by reducing an amount of an output range versus an input range.
Therefore, the conventional piecewise linear processing device illustrated in FIG. 3 uses different linear functions having different amplification rates, respectively, depending on the general environment and the low luminance environment. More specifically, the conventional piecewise linear processing device illustrated in FIG. 3 prevents noise from being excessively amplified under the low luminance environment by decreasing the amplification rate of a low code region and increasing the amplification rate of a high code region under the low luminance environment.
However, as illustrated in FIG. 4, since an image output on a screen has a drastic change at a threshold where the linear function used for the general environment changes into the linear function used for the low luminance environment, the user determines that a malfunction has occurred.